Leishmania donovani is an intracellular protozoan parasite in macrophages. How the parasite invades the host cell, circumvents being digested by lysosomes, is nourished, multiplies and eventually destroys the host cell, as well as, how the organism evades being destroyed by the host immune system are questions being asked in this study. Since the parasite surface interacts with the host plasma membrane during entry, and since parasite and host membranes constitute the primary sites of all later intracellular interactions, an understanding of the nature and physiology of these membranes is essential. Accordingly, we propose to investigate the composition and immunogenicity of the surface membranes of L. donovani amastigotes and promastigotes, as well as the nature of the membranes separating the parasite surface from the host cell cytoplasm. Results of these studies would be applicable to the in vitro assay of cell mediated responses in L. donovani infections and to work on infectivity of other hemoflagellates as Trypanosoma cruzi and African trypanosomes.